Vaccine may combat ricin attack

Ricin is a natural toxin found in castor beans

US scientists have developed a vaccine for an inhaled form of the lethal toxin ricin.

A team at the Walter Reed Army Institute of Research found all mice with a vaccine rubbed into their skin survived after inhaling the toxin.

Ricin, produced from castor beans, is 6,000 times more poisonous than cyanide and is fatal in tiny amounts.

The findings were presented at the American Society for Microbiology's Biodefense Research Meeting.

Traces of ricin were found recently in the US Senate, while last year five people were arrested after the chemical was uncovered in a North London flat.

'Fatal dose'

Dr Gary Matyas and colleagues developed a vaccine from a mutant form of ricin's 'A chain' and combined it with cholera toxin.

Ricin is made up of two components - chains A and B. The B chain binds the toxin to the cells while the A chain actually penetrates and kills them.

The vaccine was applied to an area of shaved skin on the mice. A separate group of mice received a patch made out of the same vaccine.

Both groups of mice were exposed to a lethal dose of aerosolised ricin and then boosted with the vaccine every two weeks.

Ricin is a credible threat in some circumstances, however it currently does not pose a danger to large crowds of people. Professor Peter Blain, Medical Toxicologist, Health Protection Agency

After several weeks both groups displayed high levels of anti-ricin immune responses.

Mice with the vaccine applied directly to their skin had a 100% survival rate, while the rate for those with the patch was 70%.

'Difficult to disperse'

There is currently no vaccine against ricin, which has previously been used in terrorist attacks.

Ricin can be produced quickly and cheaply from castor beans. It is fatal when injected, inhaled or ingested.

Just seventy micrograms of ricin, the equivalent to a single grain of salt, is enough to kill a person.

Symptoms of ricin exposure include fever, vomiting, diarrhoea, coughing and seizures. It usually takes about 24 hours for symptoms to appear, and death can occur within several days.

Professor Peter Blain, medical toxicologist at the Health Protection Agency said he welcomed any developments in the prevention, detection or treatment of ricin poisoning.

However, he added that as the study has only taken place in animals it would be some time before the findings could be translated into a readily available vaccine for humans.

"Ricin is a credible threat in some circumstances, however it currently does not pose a danger to large crowds of people," he said.

" It is difficult to disperse in the open air in sufficient quantities to harm large numbers."